The present invention relates in general to integrated circuits, and in particular to method and circuitry for implementing high speed output drivers that incorporate resistive series termination and pre-distortion functions.
In order to enable high speed communication, a transmitter with a high speed output driver is needed. For communication over distances appreciable with respect to the signal bit period, termination is also needed to prevent unwanted reflections that would corrupt the signal. Transmission line termination can be implemented outside of the transmitter integrated circuit. This, however, increases the external components count and the cost of the product. It is, therefore, preferred to provide a self-terminating resistive output driver that incorporates the termination. It is also desirable to eliminate or minimize inter-symbol interference (ISI) which results from a frequency bandlimited system. Pre-distortion is a useful technique which allows the transmitter to use its output driver to cancel ISI. Further, in order to keep the output driver inexpensive, it is also desirable to be able to implement the driver in conventional digital CMOS technology.
Accordingly, there is a need for a high-speed output driver circuit that operates at the highest speed possible in a digital CMOS technology, incorporates within its circuit resistive termination and pre-distortion to cancel ISI.